So I have gotten a new job at a medium sized company as an IT-administrator.

I have also inherited this monster (actually, there is 2 of them) from the previous administrator:

I'd like you guys expertise and experience on how to make sense of it. Someday, all hell will probably break loose and I'll need to fiddle with the cables and switches.

So I'll need to have an overview of where which cable leads to etc.
What approach should I take?

EDIT: I guess I did not clarify myself well enough :) I also mean that it a little more detailed. Such as, you say: Color both ends. Yes, but what is the easiest way to figure out which cable leads to where? :)

Once you differentiate between clients and infrastructure (and VLAN associations), it will be much easier to just unplug and, re-wire everything. I agree with the other posts> shorter cables would be very useful.

ADDITIONAL INFO

Per your added request for details, sounds like you need to know where to begin. Obviously, try as hard as you can to get some kind of port documentation from the previous administrator (If you're lucky!). If that's not available, you will need to:

See if the patch panels and room ports are labeled, if they are then, GREAT! start documenting!

I definately second the recommendation to get a good tone and probe tester like the one you linked to. Plugging and unplugging cables while looking to see if the light changed it unbelievably time consuming and error prone. Not to mention it's not much use for tracing inactive cables. :-) With a good tone and probe tester you should be able to find where your cable goes in minutes.
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Bob McCormickMay 12 '09 at 17:47

3

Also, if the existing deployment is already labeled, verify that the labels are accurate. I can't tell you how many places I've walked into there the labels were just plain wrong (painters move wall plates around, etc.).
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Justin ScottMay 18 '09 at 21:20

Probably most important - label both ends of each cable as to where the other end goes.

-added-

Keep a couple of long, brightly colored (ie. really ugly) cables handy somewhere, for when you need a temporary cable. They will look out of place and help you remember to replace them with properly labeled ones asap.

+1 to label both ends. Label them with non-descriptive alphanumerics so you don't stat thinking later that cable "router-1523" has anything to do with a router since it was the only cable the other guy could find one day to hook up the CEO's twittering coffeemaker.
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Adam DavisMay 12 '09 at 16:00

But what is the easiest approach to reach that goal? :)
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caspertMay 12 '09 at 16:27

Use labelling that can be removed, and remove it as soon as you remove a cable for a particular purpose. And never leave a cable connected at only one end for longer than absolutely necessary. Someone will plug it in where they shouldn't.
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dunxdDec 13 '10 at 11:04

Be aware that this is going to take HOURS UPON HOURS to get straightened out. It is long, tedious work.

My suggestion for the process in the server room ..
1- build a structure for how plugs are identified. Label as necessary to make it clear.
2- install some cable management on the rack. If you can't get or find premade ones, use cable ties, make them into loops, and connect them to the sides of the racks.
3- buy a crimper and learn how to make patch cables.
4- One by one, replace each cable with one that is routed properly, made to length, and labeled at BOTH ends, each having BOTH ends identified.
5- Don't move/reuse cables. If something moves, cut the ends, re-make and re-label the cable. You can re-use a cut cable for a shorter one .. my point is to make sure that you don't have mis-labeled or over-length cables in the rack.

I have found that color coded patch cables are over-rated, except for the very few (< 5%) key cables that are only to be touched in an emergency. Examples are the cable from the switch to the internet router, or from the switch to the mail server.

The idea of having some odd colored temp cables is excellent, provided you have the discipline to swing back and replace them correctly.

NOTE: Others will disagree with the idea of making your own patch cables. My conclusion is that the added risk of cable failure is outweighed by the gain from properly routed cables for all but the critical cables I mention in the color coding note.

If the problem is that you don't know WHERE the cables lead, here would be how I might approach it.

First, make sure all drops on the front of the patch panel are labeled properly, with unique numbers or alpha-# labels.

Next, you will probably need to get the assistance of someone after hours and get a walkie talkie and a labeler. Tell all users to leave all PCs and ethernet-connected equipment on when they leave.

Have your helper walk around with the walkie talkie and labeler. Have them unplug one device at a time. You look at your hubs\switches and check which link light goes out. Trace from there to your patch panel, and radio you helper to label the drop with whatever number you already have on your patch panel.

This will match up all drops in the office to each patch panel.

Now as far as cables going to and from stuff inside the computer room \ rack, you pretty much have to physically trace it or do the same thing as you outside drops and disconnect cables and look for link light drops to see what is being disconnected.

You can use Sticky notes to temp label cables until you print out proper lables, and I agree, cables not going outside of the computer room should be labled at both ends.

Also .. if you do need to trace your drops remote ethernet cable testers are pretty inexpensive, and you might as well plug one in to help you find out if any drops are bad..

Trace each cable and make a list of what device and port # goes where. To clean this up, you can get some cable channels and organizers for the rack (from blackbox or any number of other places). I would come in late at night or on the weekend and just move plugs one at a time to get them better organized.

Also, you can get stickers with numbers (electricians, etc use these) to put on each end. So the cable becomes "#114", and you maintain a list of what each number is for.

Your best bet for tracing the short cables is just to follow them by hand.

For longer cables, or to sort out network drops, get a tone generator and hook it up to the remote end of the cable, and use the tone detector at this end to determine which cable is carrying the signal.

For cabling inside a server room from rack to rack, I HIGHLY recommend the AMP NETCONNECT MRJ21 System. It's like an extension cord for your switch. You only have to run 6 semi-thick cables instead of 48 CAT6 cables (4 cables if you aren't doing gigabit). Or instead of having a switch in the rack that connects back to the backbone, you connect directly to the backbone thus not losing speed.

I usually use 1-foot patch cables and put the patch panel right above the switch. This allows me to only have to worry about cable management on uplinks. It helps if the patch panel and switch are the same density like both are 48-ports and each 1U.

Get a tape labeller (e.g. one by Brother) and a bunch of different sized tapes. I much prefer the TZS tapes that have stronger adhesive for labelling cables.

As mentioned in other answers, the first step is to map out and label what's on the other end of each port (if you don't already have this).

At one point we made things clearer by color-coding our cables. Most office connections were grey, cross-connects were purple, special connections that were in the DMZ or outside the firewall were red and yellow. In the server room, servers used blue cables if they were inside the firewall, red in the DMZ, and the external connections were in red. Cross-over cables were only orange.

I'd say it's better to shut everything down, take out all the existing cables and re-do it all properly. We cleaned up our server room one afternoon when we had a campus-wide power outage and everyone had to be sent home because the fire system wasn't working.

Get a bunch of double-sided velcro: hooks on one side, loops on the other (I didn't find the gardening stuff to be strong enough) and use it all over the place. When we re-did our remote wiring closets, each group of 3-6 patch cables that ran in the same direction was bundled together at several points. Yeah, it's a bit more time when you add or remove one, but it's a lot easier to get the ones you aren't working with out of the way.

Get a documentation and keep it up to date. Excel is fine, I've also seen an admin who's built an HTML Map (like the kind where you get an alt for mouse overs of specific image parts). Its probably a lot of work, but I liked it a lot for you get a good view of the whole situation.
Another thing I've seen in a datacenter was actual tags hanging from cables. Deepending on how big of a mess you have after cleaning this up, that might also be a good idea, because it would mean to have your documentation right there, where it belongs - on each cable in the rack.

You should definitely make those shorter and color coded cables as has been stated. Also think about maybe grouping cables, like Servers go on the same patch panel and switch, clients go in groups by floors or whatever to their panels and switches. That makes it a lot easier to separate stuff and would allow you to use cable fixers to hold cables together by those groups.